1. Field of the Invention
The present invention relates generally to electronic fuel injection systems for internal combustion engines in automotive vehicles and, more particularly, to a method of feedback control for an electronic fuel injection system in an internal combustion engine for an automotive vehicle.
2. Description of the Related Art
Modern automotive vehicles have an exhaust system which includes a three-way catalyst to reduce HC, CO and NO.sub.x emissions from an internal combustion engine in the vehicle simultaneously if the fuel/air ratio of the feedgas to the engine is maintained within a narrow window. To accomplish this, automotive vehicles have used a single O.sub.2 sensor located upstream of the catalyst for fuel/air feedback control.
With the current single O.sub.2 sensor for feedback control, a voltage output signal of the O.sub.2 sensor (which has a non-linear proportionality to the fuel/air ratio) is compared to a calibrateable voltage threshold to determine if the fuel/air ratio is rich or lean. When the voltage output signal is determined to switch from lean to rich (for example, to go from below to above the O.sub.2 sensor switch point calibration), an O.sub.2 controller kicks lean and beings to ramp lean until the O.sub.2 sensor voltage output signal changes from rich to lean. Then, the O.sub.2 controller kicks rich and begins to ramp rich until the O.sub.2 sensor voltage output signal changes again from lean to rich.
While the use of the current single O.sub.2 sensor has worked well, the O.sub.2 sensor is subject to both short and long term errors that affect fuel/air control. The short term errors are due to shifts in the O.sub.2 sensor voltage output signal based on exhaust gas temperature and composition. The long term errors are due to high exhaust gas temperatures and to potentially poisonous exhaust emissions. These factors can lead to a slowed O.sub.2 sensor response, and a shift in the voltage of the output signal relative to the fuel/air ratio with time.